This invention relates generally to adhesive attachment assemblies or fixtures and related methods for securing an adhesive attachment or the like to a supporting surface or substrate. More specifically, this invention relates to improvements in such adhesive attachment assemblies or fixtures, of the general type shown and described in U.S. Pat. Nos. 4,302,492; 4,338,151; 4,390,546; 4,668,546; 4,778,702; and 4,822,656, and particularly with respect to providing a simplified attachment configuration wherein post-installation removal of a separate mounting or support fixture is not required.
In many instances, it is necessary or desirable to attach an attachment component or element such as a patch, threaded screw, or other structure onto a supporting substrate. For example, it may necessary to apply a thin patch to the skin of an aircraft or to the hull of a boat to repair a hole therein. Alternately, it may be desirable to mount a threaded stud or other device onto a substrate, for example, the windshield of an automobile, without requiring a hole to be made in the substrate. In many such cases, it is necessary for the attachment component to be located on the substrate with relatively high precision and further that a positive force be applied urging the attachment component against the substrate for at least some minimum time period to allow, for example, curing of an adhesive bonding agent such as a curable epoxy or the like to achieve a substantially optimized and secure bond with the substrate.
In the past, many different clamp and fixture devices have been proposed for use in temporarily holding an attachment component on the surface of a substrate during the cure time of a bonding agent. The majority of such clamp and fixture devices have required some form of mechanical connection to the substrate by means of screws or other mechanical fasteners, clamping jaws, etc. However, these devices are not suited for use with extended surface areas or for use with fragile or thin-walled substrates within which surface interruptions to accommodate mechanical fastening are not possible or desirable. Other fixturing devices have been proposed which rely upon suction cups for holding an attachment component in position on a substrate, but suction cup devices are limited to use with relatively smooth-surfaced substrates and further function to retain the attachment component in place without exerting significant positive forces urging the attachment component against the substrate. As a result, with suction cup devices, the bonding agent on the substrate can be unevenly distributed and/or cure with less than optimum bond strength.
Improved adhesive attachment devices are described and claimed in U.S. Pat. Nos. 4,302,492; 4,338,151; 4,390,546; 4,668,546; 4,778,702; and 4,822,656. More particularly, these devices disclose attachment devices having a support fixture for temporary securement to the substrate by means of a pressure sensitive adhesive or the like, in combination with force bias or spring means for applying a force urging the attachment component into positive bearing engagement with the substrate for the cure time duration of a selected adhesive bonding agent. The support fixture or a portion thereof is movable between a first position with the adhesive component substantially out of bearing engagement with the substrate to a second position with the attachment component pressed firmly against the substrate. An over-center mechanism constitutes the movable element in most of the described embodiments. Following curing of the adhesive bonding agent, the support fixture is removed from the substrate to leave the attachment component such as a threaded bolt or the like securely bonded to the substrate. In this regard, the pressure sensitive adhesive has a sufficient adhesion strength for retaining the attachment component in position during curing of the bonding agent, but insufficient adhesion strength to preclude subsequent tear-off removal of the support fixture from the substrate.
While the improved attachment devices described in the above referenced patents offer significant advantages in comparison with the previous art, they have each required the support fixture which must be removed and is typically discarded after the selected adhesive bonding agent has cured.
The present invention relates to an improved and relatively simplified adhesive attachment wherein removal of a support fixture component from the substrate following curing of the adhesive bonding agent is not required.
In accordance with the invention, a self fixturing adhesive attachment is provided for securely mounting an attachment component such as a threaded stud or the like relative to the surface of a substrate. The self fixturing attachment comprises, in one preferred form, a base fixture carrying the attachment component and defining a base surface for receiving a selected bonding agent thereon. A resilient pressure sensitive adhesive member has a first portion carried by the attachment component at a blind side thereof, a second portion secured to the base fixture, and a third portion extending therebetween. Upon pressed mounting of the base fixture with the bonding agent thereon onto the surface of the substrate, the attachment component is movable to press the first portion of the pressure sensitive adhesive member into adherence with the substrate, resulting in stretched elongation of the third portion thereof to pull the base fixture with a positive force toward the substrate for the duration of the bonding agent cure time.
In a preferred form, the base fixture comprises a disk which is centrally dished to define a shallow cavity at a blind side thereof, and wherein this shallow cavity is circumscribed by a generally annular attachment or base surface. The attachment component comprises a threaded bolt or the like having an enlarged head seated within said disk cavity in a position generally circumscribed by the annular base surface, and a threaded shank protruding through a central disk port to a front side of the base fixture. A bolt shoulder of noncircular or square cross section or the like is positioned within the disk port which has a mating noncircular or square cross sectional shape or the like to prevent relative rotation between the attachment component and the base fixture. The pressure sensitive adhesive member comprises, in the preferred form, a layer of a pressure sensitive elastomer such as that marketed by 3M Company of Minneapolis, Minn. under the designation VHB Type 4910 Tape, having elastomeric bulk properties permitting about 100% elongation without tearing and high strength acrylic pressure sensitive adhesive on opposed surfaces. This adhesive layer includes the first portion comprising a central region adhered to a blind side of the bolt head, the second portion comprising a peripheral margin adhered to the base fixture at an annular recessed shoulder formed within the disk cavity, and an annular third portion extending therebetween.
The selected adhesive bonding agent is applied to the annular attachment or base surface at the blind or underside of the base fixture, and the base fixture is then press-mounted onto the substrate at a selected location. In this initial mounted position, the pressure sensitive adhesive layer is supported in an unstressed state by the base fixture and the attachment component, with the adhesive layer retracted or spaced at least slightly from the adjacent surface of the substrate. The attachment component is then movable relative to the base fixture to press the first portion or central region of the adhesive layer into firm pressure sensitive adherence with the substrate. This displaces the first portion of the adhesive layer out of alignment with the second portion or peripheral margin thereof, resulting in stretched elongation of the intermediate third layer portion to apply the desired force pulling the base fixture positively against the substrate for the duration of the bonding agent cure time. Thereafter, the base fixture supports and anchors the attachment component securely on the substrate for normal use.
In one alternative preferred form, the pressure sensitive adhesive member may be substituted by temporary attachment means such as a pointed nail for securing the attachment component to the substrate, in combination with spring means acting between the attachment component and the base fixture for applying a positive force urging the base fixture against the substrate for the duration of the bonding agent cure time. In this embodiment, following pressed mounting of the base fixture with bonding agent thereon onto the substrate, the attachment component such as a threaded bolt can be impact driven against the substrate for connecting the bolt head to the substrate. In one form, the temporary attachment means comprises a concrete nail carried on the bolt head for penetrating a concrete substrate. The spring means comprises a leaf spring or the like reacting between the threaded bolt and the base fixture, for positively urging the base fixture toward the substrate following connection of the bolt head to the substrate.
In a further alternative preferred form of the invention, the base fixture may comprise the functional element of the self fixturing adhesive attachment, wherein the attachment component supported thereby provides means for urging the base fixture against the substrate with a positive force for the cure time of a selected bonding agent. In this embodiment, the attachment component comprises a button carried by the base fixture for movement between a normal position retracted slightly from the substrate, upon initial pressed mounting of the base fixture with bonding agent thereon against the substrate, and an advanced position pressed firmly against the substrate. In the advanced position, the button presses a first portion of a resilient pressure sensitive adhesive member against the substrate in the manner previously described, resulting in stretched elongation of a third portion thereof to pull the base fixture against the substrate with a positive force. Alternately, or in addition, a temporary attachment means such as a pointed nail in combination with spring means may be provided in the manner previously described for positively urging the base fixture against the substrate. In one preferred form, the base fixture may comprise an electrical junction box or the like, with multiple buttons carried thereby for pulling the junction box against the substrate with a positive force for the cure time of the bonding agent.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.